Fuel injection systems deliver fuel to the combustion chamber of a gas turbine engine, where the fuel is mixed with air before combustion. One form of fuel injection system well-known in the art utilises fuel spray nozzles. These atomise the fuel to ensure its rapid evaporation and burning when mixed with air.
An airblast atomiser nozzle is a type of fuel spray nozzle in which fuel delivered to the combustion chamber by one or more fuel injectors is aerated by air swirlers to ensure rapid mixing of fuel and air, and to create a finely atomised fuel spray. The swirlers impart a swirling motion to the air passing therethrough, so as to create a high level of shear and hence acceleration of the low velocity fuel film.
Typically, an airblast atomiser nozzle has a number of coaxial air swirler passages. An annular fuel passage between a pair of air swirler passages feeds fuel onto a prefilming lip, whereby a sheet of fuel develops on the lip. The sheet breaks down into ligaments which are then broken up into droplets within the shear layers of the surrounding highly swirling air to form the fuel spray stream that enters the combustor.
Hot combustion gases can produce high metal temperatures in the nozzle, leading to degradation of the nozzle and a reduced service life. In particular, in nozzles having a coaxial arrangement of an inner pilot airblast fuel injector, an intermediate air swirler passage and an outer mains airblast fuel injector, high metal temperatures can be problem for a wall of the intermediate air swirler passage.
It is desirable to provide a fuel spray nozzle that is less susceptible to high metal temperatures.